1. Field of the Invention
The present invention relates to power conversion systems, and more particularly to an aircraft architecture and a multiple function power converter for an aircraft.
2. Description of the Related Art
Electric systems used in complex environments such as aerospace systems, more electric aircraft systems, industrial environments, vehicles, etc., include a large number of electric systems and modules. During operation of such complex environments, various electric systems and modules may need to be connected to electric power sources, disconnected from electric power sources, maintained in a powered-up state, etc., at various times. Moreover, various electric systems and modules in a complex environment may require different amounts and type of electrical power. For example, some electric systems and modules may require DC power while others may require AC power. Some electric systems and modules may require 28V dc, others 230V ac, yet others 115V ac at 400 Hz. The power levels required by various parts of a complex environment may also depend on the operational stage of the environment. For example, different levels of power may be needed during the start-up and during the continuous operation of a complex environment, such as an aircraft.
Aircraft are currently being designed to use less non-electric power (such as hydraulic and pneumatic power) and more electrical power. Aircraft system architectures that rely solely, or to a great extent, on electrical power, are also referred to as More Electric Aircraft (MEA) system architectures. Typically, MEA system architectures use starter generators to start the aircraft main engines as well as to supply electrical power to various system loads. These various system loads may utilize electrical power at various frequencies and voltages. Hence, many MEA system architectures, and/or starter generators currently used to power MEA system architectures, typically include relatively complex power electronics circuits with large weight. For example, some systems may include inverters, for converting DC to AC power, auto-transformer rectifier units (ATRUs) for converting AC power to DC power, and potentially complex voltage and frequency control circuits, which can increase overall complexity, cost, and maintenance.
An aircraft architecture that uses electric power for engine start and for other modules such as the Environmental Control System (ECS), requires a number of components to perform AC-DC and controlled DC-AC power conversion. These conversion components, together with their associated contactors, add significant weight and complexity to the aircraft. Components typically used to perform the AC-DC power conversion in complex systems such as aircraft systems are Transformer-Rectifiers Units (TRUs) or ATRUs. Both the TRUs and the ATRUs are large and bulky units.
One power system architecture for aircraft using ATRUs and TRUs is described in patent application US 2004/0129835 A1, by W. Atkey et al. In this patent application, an electric power distribution system includes AC generators. High voltage AC power can be converted to high voltage DC power by one or more AC-to-DC conversion devices, such as ATRUs, that receive AC power from AC busses. Using the ATRUs, the power distribution system provides high voltage AC and DC power to support conventional 115V and 28V dc bus architectures. During start, each AC generator is supplied by a dedicated start converter. During normal operation, each motor load, such as, for example, each air compressor motor, is supplied by a dedicated motor controller.
Complex electrical systems, such as variable frequency AC systems used in some MEA architectures, impose design constraints on the generating and conversion aircraft equipment, since the electromagnetic design of aircraft units that are part of the electrical power system, is heavily dependent upon the minimum frequency used. Some limited applications of high voltage DC distribution systems have attempted to relieve some of these design constraints. However, use of such high voltage DC distribution systems on large commercial aircraft has been hindered because of concerns over arc dissipation during faults, corona effect, and significant risks associated with the servicing of high power and high voltage DC systems.
Hence, the generating and conversion systems employed so far in the aerospace and related industries are sub-optimal, since the cost, weight, and reliability tradeoffs have not been favorable for many types and sizes of aircraft.
Disclosed embodiments of this application address these and other issues by utilizing a multiple function power converter in one embodiment, to perform multiple functions in the generating and conversion system of a large system such as an aircraft. The multiple function power converter performs the functions of a start converter, an ECS motor controller, a motor controller for other loads, and a static inverter to obtain a frequency that can be constant, hence eliminating dedicated converters, controllers and inverters. In another embodiment, an electric system architecture is implemented. The electric system architecture consists of a high voltage, high frequency generating and distribution system, resulting in lower size and weight. Frequency insensitive utilization equipment is directly connected to a high frequency bus. The majority of the utilization equipment is supplied through power conversion devices such as motor controllers, frequency converters, or transformer rectifiers. The high frequency output of the power generating system is rectified using AC/DC converters, such as rectifier bridges, located at the input of each of the power converters in the system. Centralized and distributed rectification architectures are presented in the current application. In a centralized rectification architecture, one rectifier is connected at the input of multiple power converters, while in a distributed rectification architecture, a different rectifier is connected at the input of each power converter. The centralized and distributed rectification architectures presented in the current application eliminate large ATRUs and TRUs from the aircraft generating and distribution system. Multiple function power converters may be used as controllers, converters and inverters in the electric system architecture, to realize more space and weight savings and increase efficiency of the generating and distribution system.